1. Field of the Invention
This invention relates to curable organosiloxane compositions. More particularly, this invention relates to organosiloxane compositions that cure by a platinum-catalyzed hydrosilylation reaction and contain the catalyst encapsulated within particles of a polysilane resin or silicone resin to provide excellent storage stability at room temperature and rapid curing above the softening temperature of the resin. The compositions yield highly heat-resistant elastomer moldings.
Background Information
Organosiloxane compositions that cure by a hydrosilylation reaction are distinguished by a rapid cure in deep sections without the development of reaction by-products. These compositions find application in a wide range of fields as, for example, molding rubbers, adhesives, potting agents for electrical and electronic products, coatings, and release coatings for papers and films.
Curable organosiloxane compositions containing a platinum-containing catalyst that is embedded or microencapsulated within a layer of silicone resin are known. Specifically, U.S. Pat. No. 4,481,341, which issued to Schlak et al. on Nov. 6, 1984 describes curable organosiloxane compositions containing a finely divided blend of a platinum-containing catalyst and a silicone resin.
The use of silicone resins and polysilane resins to microencapsulate platinum-containing catalysts for curable organosiloxane composition is disclosed in commonly assigned copending U.S. patent applications Ser. No. 370,418, U.S. Pat. No. 5,015,716, and application Ser. No. 370,419, filed on Jun. 22, 1989, now abandoned.
The present inventors discovered that compositions containing hdyrosilylation reaction catalysts that are microencapsulated within a layer of silicone or polsilane resin exhibit excellent storage stability in the neighborhood of room temperature. However, when the cured elastomer molding is subjected to long-term heating the silicone resin or polysilane resin coagulates within the body of the molding. In addition to being undesirable from the standpoint of appearance, the coagulated resin adversely affects the mechanical strength of the elastomer molding.
The present inventors carried out extensive research directed at a solution to the aforementioned problem, and they discovered as a result that when a member of a specified group of metal compounds is blended into an curable organosiloxane composition containing a platinum-containing or other type of hydrosilylation catalyst microencapsulated in a silicone or polysilane resin, the resin does not coagulate even when the cured elastomer molding is subjected to long-term heating.
An objective of the present invention is to provide a curable organosiloxane composition exhibiting 1) excellent storage stability in the vicinity of room temperature by virtue of a microencapsulated platinum-containing catalyst and 2) the absence of coagulation during long term heating of the silicone or polysilane resin used as the encapsulating material for the platinum-containing catalyst, and therefore at most a slight reduction in the mechanical strength of elastomeric articles molded from the curable composition.